1. Field of the Invention
The invention relates to a heat exchanger having flat pipes arranged mutually parallel and spaced apart from one another, which are connected via connecting apertures formed on their narrow sides to corresponding connecting apertures of respective collector pipes for flow and re-flow by welding together the flat pipes with the collector pipes.
2. Description of the Prior Art
In the known heat exchangers of this type flat pipes are arranged such, that the pipes run parallel and at a distance from one another. In view of the technology applied in their production, customary flat pipes with relatively large volumes of water are used, because a sufficient width along the narrow side of the flat pipes for the formation of adequately dimensioned connecting apertures has to be provided. The width must be sufficient to obtain an acceptable stable connection of the flat pipes to the collector pipes by welding such as projection welding.
If the heat exchanger is used as a heating body in a central heating plant and hot water flows through the flat pipes at a high rate of flow resulting in a reduced thermal inertia of the heating body and thereby a better heat transmission, an improved utilization of the consumed energy can be accomplished. In order to achieve this effect in a heat exchanger of the kind described above, ultraflat oval shaped pipes are applied through which the water flows at a higher rate of flow. Ultraflat pipes may be defined as pipes which have a ratio of the surface area of the internal cross-section to the external circumference smaller than or equal to 2.5. The depth of such flat pipes is too small to allow the creation of sufficiently large connection apertures on their narrow sides which are necessary to ensure the flow of hot water from the collector pipes to the flat pipes or in the reverse direction. Moreover, the small depth of the flat pipes does not allow the creation of an adequately strong joint on their narrow sides by the customary welding methods to ensure the necessary stability of the heat exchanger.
The object of the invention is, therefore, to provide a heat exchanger of the kind described, that can be manufactured by known welding methods, to achieve a better utilization of consumed energy. To save energy, flat pipes with very small depths can be used. This objective is achieved by shaping a wall portion around each connection aperture of each flat pipe to correspond to a mating wall portion of the collector pipes.